Hydrocarbon dehydrocyclization with an acidic multimetallic catalytic composite

ABSTRACT

Dehydrocyclizable hydrocarbons are converted to aromatics by contacting them at hydrocarbon dehydrocyclization conditions with an acidic multimetallic catalytic composite comprising a combination of catalytically effective amounts of a platinum group component, a pyrolyzed ruthenium carbonyl component, a rhenium component, and a halogen component with a porous carrier material. The platinum group, ruthenium, rhenium and halogen components are present in the multimetallic catalyst in amounts respectively, calculated on an elemental basis, corresponding to about 0.01 to about 2 wt. % platinum group metal, about 0.01 to about 2 wt. % carbonyl-derived ruthenium, about 0.01 to about 5 wt. % rhenium, and about 0.1 to about 3.5 wt. % halogen. A key feature associated with the preparation of the subject catalytic composite is reaction of a ruthenium carbonyl complex with a porous carrier material containing a uniform dispersion of a platinum group component maintained in the elemental state, whereby the interaction of the ruthenium moiety with the platinum group moiety is maximized due to the platinophilic (i.e. platinum-seeking) propensities of the carbon monoxide ligand used in the ruthenium reagent.

CROSS-REFERENCES TO RELATED DISCLOSURES

This application is a continuation-in-part of my prior copendingapplication Ser. No. 246,828 filed Mar. 23, 1981, which in turn is adivision of my prior application Ser. No. 82,436 filed Oct. 5, 1979, andissued May 19, 1981 as U.S. Pat. No. 4,268,377, which in turn is acontinuation-in-part of my prior application Ser. No. 848,699 filed Nov.4, 1977, and issued Jan. 15, 1980 as U.S. Pat. No. 4,183,804. All of theteachings of these prior applications are specifically incorporatedherein by reference.

BRIEF SUMMARY OF THE INVENTION

The subject of the present invention is, broadly, an improved method fordehydrocyclizing a dehydrocyclizable hydrocarbon to produce an aromatichydrocarbon. In a narrower aspect, the present invention involves amethod of dehydrocyclizing aliphatic hydrocarbons containing 6 to 20carbon atoms per molecule to monocyclic aromatic hydrocarbons withminimum production of side products such as C₁ to C₅ hydrocarbons,bicyclic aromatics, olefins and coke. In another aspect, the presentinvention relates to the dehydrocyclization use of an acidicmultimetallic catalytic composite comprising a combination ofcatalytically effective amounts of platinum group component, a pyrolyzedruthenium carbonyl component, a rhenium component, and a halogencomponent with a porous carrier material. This acidic multimetalliccomposite has been found to possess highly beneficial characteristics ofactivity, selectivity, and stability when it is employed in thedehydrocyclization of dehydrocyclizable hydrocarbons to make aromaticssuch as benzene, toluene and xylene.

The conception of the present invention followed from my search for anovel catalytic composite possessing a hydrogenation-dehydrogenationfunction, a controllable cracking and isomerization function, andsuperior conversion, selectivity, and stability characteristics whenemployed in hydrocarbon conversion processes that have traditionallyutilized dual-function catalytic composites. In my prior application, Idisclosed a significant finding with respect to a multimetalliccatalytic composite meeting these requirements. More specifically, Idetermined that a combination of specified amounts of a pyrolyzedruthenium carbonyl component and a rhenium component can be utilized,under certain conditions, to beneficially interact with the platinumgroup component of a dual-function acidic catalyst with a resultantmarked improvement in the performance of such a catalyst. Now I haveascertained that an acidic multimetallic catalytic composite, comprisinga combination of catalytically effective amounts of a platinum groupcomponent, a pyrolyzed ruthenium carbonyl component, a rhenium componentand a halogen component with a porous carrier material, can havesuperior activity, selectivity, and stability characteristics when it isemployed in a ring-closure or dehydrocyclization process if thecatalytically active sites induced by these components are uniformlydispersed in the porous carrier material in the amounts specifiedhereinafter and if the oxidation state of the active metallicingredients are carefully controlled so that substantially all of theplatinum group component is present in the elemental metallic stateduring incorporation of the ruthenium carbonyl component.

The dehydrocyclization of dehydrocyclizable hydrocarbons is an importantcommercial process because of the great and expanding demand foraromatic hydrocarbons for use in the manufacture of various chemicalproducts such as synthetic fibers, insecticides, adhesives, detergents,plastics, synthetic rubbers, pharmaceutical products, high octanegasoline, perfumes, drying oils, ion-exchange resins, and various otherproducts well known to those skilled in the art. One example of thisdemand is in the manufacture of alkylated aromatics such asethylbenzene, cumene and dodecylbenzene by using the appropriatemono-olefins to alkylate benzene. Another example of this demand is inthe area of chlorination of benzene to give chlorobenzene which is thenused to prepare phenol by hydrolysis with sodium hydroxide. The chiefuse for phenol is of course in the manufacture of phenol-formaldehyderesins and plastics. Another route to phenol uses cumene as a startingmaterial and involves the oxidation of cumene by air to cumenehydroperoxide which can then be decomposed to phenol and acetone by theaction of an appropriate acid. The demand for ethylbenzene is primarilyderived from its use to manufacture styrene by selectivedehydrogenation; styrene is in turn used to make styrene-butadienerubber and polystyrene. Orthoxylene is typically oxidized to phthalicanhydride by reaction in vapor phase with air in the presence of avanadium pentoxide catalyst. Phthalic anhydride is in turn used forproduction of plasticizers, polyesters and resins. The demand forpara-xylene is caused primarily by its use in the manufacture ofterephthalic acid or dimethyl terephthalate which in turn is reactedwith ethylene glycol and polymerized to yield polyester fibers.Substantial demand for benzene also is associated with its use toproduce aniline, Nylon, maleic anhydride, solvents and the likepetrochemical products. Toluene, on the other hand, is not, at leastrelative to benzene and the C₈ aromatics, in great demand in thepetrochemical industry as a basic building block chemical; consequently,substantial quantities of toluene are hydrodealkylated to benzene ordisproportionated to benzene and xylene. Another use for toluene isassociated with the transalkylation of trimethylbenzene with toluene toyield xylene.

Responsive to this demand for these aromatic products, the art hasdeveloped a number of alternative methods to produce them in commercialquantities. One method that has been widely studied involves theselective dehydrocyclization of a dehydrocyclizable hydrocarbon bycontacting the hydrocarbon with a suitable catalyst atdehydrocyclization conditions. As is the case with most catalyticprocedures, the principal measure of effectiveness for thisdehydrocyclization method involves the ability to perform its intendedfunction with minimum interference of side reactions for extendedperiods of time. The analytical terms used in the art to broadly measurehow well a particular catalyst performs its intended functions in aparticular hydrocarbon conversion reaction are activity, selectivity,and stability, and for purposes of discussion here, these terms aregenerally defined for a given reactant as follows: (1) activity is ameasure of the catalyst's ability to convert the hydrocarbon reactantinto products at a specified severity level where severity level meansthe specific reaction conditions used--that is, the temperature,pressure, contact time, and presence of diluents such as H₂ ; (2)selectivity usually refers to the amount of desired product or productsobtained relative to the amount of the reactant charged or converted;(3) stability refers to the rate of change with time of the activity andselectivity parameters--obviously the smaller rate implying the morestable catalyst. More specifically, in a dehydrocyclization process,activity commonly refers to the amount of conversion that takes placefor a given dehydrocyclizable hydrocarbon at a specified severity leveland is typically measured on the basis of disappearance of thedehydrocyclizable hydrocarbon; selectivity is typically measured by theamount, calculated on a weight percent of feed basis or on a molepercent of converted dehydrocyclizable hydrocarbon basis, of the desiredaromatic hydrocarbon or hydrocarbons obtained at the particular activityor severity level; and stability is typically equated to the rate ofchange with time of activity as measured by disappearance of thedehydrocyclizable hydrocarbon and of selectivity as measured by theamount of desired aromatic hydrocarbon produced. Accordingly, the majorproblem facing workers in the hydrocarbon dehydrocyclization orring-closure art is the development of a more active and selectivecatalytic composite that has good stability characteristics.

I have now found a dual-function acidic multimetallic catalyticcomposite which possesses improved activity, selectivity, and stabilitywhen it is employed in a process for the dehydrocyclization ofdehydrocyclizable hydrocarbons. In particular, I have determined thatthe use of an acidic multimetallic catalyst comprising a combination ofcatalytically effective amounts of platinum group component, a pyrolyzedruthenium carbonyl component, a rhenium component and a halogencomponent with a porous refractory carrier material can enable theperformance of a hydrocarbon dehydrocyclization process to besubstantially improved. Moreover, particularly good results are obtainedwhen this catalyst is prepared and maintained, during use in thedehydrocyclization method, in a substantially sulfur-free state. Thisacidic multimetallic catalytic composite is particularly useful in thedehydrocyclization of C₆ to C₁₀ paraffins to produce aromatichydrocarbons such as benzene, toluene, and the xylenes with minimizationof by-products such as C₁ to C₅ saturated hydrocarbons, bicyclicaromatics, olefins and coke.

In sum, the current invention involves the significant finding that acombination of a pyrolyzed ruthenium carbonyl component and a rheniumcomponent can be utilized under the circumstances specified herein tobeneficially interact with and promote an acidic dehydrocyclizationcatalyst containing a platinum group metal when it is used in theproduction of aromatics by ring-closure of aliphatic hydrocarbons.

It is, accordingly, one object of the present invention to provide anovel method for the dehydrocyclization of dehydrocyclizablehydrocarbons utilizing an acidic multimetallic catalytic compositecomprising catalytically effective amounts of a platinum groupcomponent, a pyrolyzed ruthenium carbonyl component, a rhenium componentand a halogen component combined with a porous carrier material. Asecond object is to provide a novel acidic catalytic composite havingsuperior performance characteristics when utilized in adehydrocyclization process. Another object is to provide an improvedmethod for the dehydrocyclization of paraffin hydrocarbons to producearomatic hydrocarbons which method minimizes undesirable by-productssuch as C₁ to C₅ saturated hydrocarbons, bicyclic aromatics, olefins andcoke.

In brief summary, one embodiment of the present invention involves amethod for dehydrocyclizing a dehydrocyclizable hydrocarbon whichcomprises contacting the hydrocarbon at hydrocarbon dehydrocyclizationconditions with an acidic multimetallic catalytic composite comprising aporous carrier material containing a uniform dispersion of catalyticallyeffective amounts of a platinum group component, pyrolyzed rutheniumcarbonyl component, a rhenium component, and a halogen component.Further, these components are present in this composite in amounts,calculated on an elemental basis, sufficient to result in the compositecontaining about 0.01 to about 2 wt. % platinum group metal, about 0.01to about 2 wt. % carbonyl-derived ruthenium, about 0.01 to about 5 wt. %rhenium and about 0.1 to about 3.5 wt. % halogen.

A second embodiment relates to the dehydrocyclization method describedin the first embodiment wherein the dehydrocyclizable hydrocarbon is analiphatic hydrocarbon containing 6 to 20 carbon atoms per molecule.

A highly preferred embodiment comprehends the dehydrocyclization methodcharacterized in the first embodiment where-in the catalyst is preparedand maintained in a sulfur-free state and wherein the contacting isperformed in a substantially sulfur-free environment.

Another embodiment relates to the catalytic composite used in the first,second or third embodiments and involves the further limitation that thehalogen component is chlorine.

Other objects and embodiments of the present invention involve specificdetails regarding essential and preferred catalytic ingredients,preferred amounts of ingredients, suitable methods of multimetalliccomposite preparation, suitable dehydrocyclizable hydrocarbons,operating conditions for use in the dehydrocyclization process, and thelike particulars. These are hereinafter given in the following detaileddiscussion of each of these facets of the present invention.

Regarding the dehydrocyclizable hydrocarbon that is subjected to themethod of the present invention, it can in general be an aliphatichydrocarbon or substituted aliphatic hydrocarbon capable of undergoingring-closure to produce an aromatic hydrocarbon. That is, it is intendedto include within the scope of the present invention, thedehydrocyclization of any organic compound capable of undergoingring-closure to produce an aromatic hydrocarbon containing the same, orless than the same, number of carbon atoms than the reactant compoundand capable of being vaporized at the dehydrocyclization temperaturesused herein. More particularly, suitable dehydrocyclizable hydrocarbonsare: aliphatic hydrocarbons containing 6 to 20 carbon atoms per moleculesuch as C₆ to C₂₀ paraffins, C₆ to C₂₀ olefins and C₆ to C₂₀polyolefins. Specific examples of suitable dehydrocyclizablehydrocarbons are: (1) paraffins such as n-hexane, 2-methylpentane,3-methylpentane, 2,2-dimethylbutane, n-heptane, 2-methylhexane,3-ethylpentane, 2,2-dimethylpentane, n-octane, 2-methylheptane,3-ethylhexane, 2,2-dimethylhexane, 2-methyl-3-ethylpentane,2,2,3-trimethylpentane, n-nonane, 2-methyloctane, 2,2-dimethylheptane,n-decane and the like compounds; (2) olefins such as 1-hexene,2-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene and the likecompounds; and, (3) diolefins such as 1,5-hexadiene,2-methyl-2,4-hexadiene, 2,6-octadiene and the like diolefins.

In a preferred embodiment, the dehydrocyclizable hydrocarbon is aparaffin hydrocarbon having about 6 to 10 carbon atoms per molecule. Forexample, paraffin hydrocarbons containing about 6 to 8 carbon atoms permolecule are dehydrocyclized by the subject method to produce thecorresponding aromatic hydrocarbon. It is to be understood that thespecific dehydrocyclizable hydrocarbons mentioned above can be chargedto the present method individually, in admixture with one or more of theother dehydrocyclizable hydrocarbons, or in mixture with otherhydrocarbons such as naphthenes, aromatics, C₁ to C₅ paraffins and thelike. Thus mixed hydrocarbon fractions, containing significantquantities of dehydrocyclizable hydrocarbons that are commonly availablein a typical refinery, are suitable charge stocks for the instantmethod; for example, highly paraffinic straight run naphthas, paraffinicraffinates from aromatic extraction or adsorption, C₆ to C₉paraffin-rich streams and the like refinery streams. An especiallypreferred embodiment involves a charge stock which is a paraffin-richnaphtha fraction boiling in the range of about 140° to about 400° F.Generally, best results are obtained with a charge stock comprising amixture of C₆ to C₉ paraffins, and especially C₆ to C₉ normal paraffins.

The acidic multimetallic catalyst used in the present dehydrocyclizationmethod comprises a porous carrier material having combined therewithcatalytically effective amounts of a platinum group component, apyrolyzed ruthenium carbonyl component, a rhenium component, and ahalogen component.

Considering first the porous carrier material utilized in the presentinvention, it is preferred that the material be a porous, adsorptive,high-surface area support having a surface area of about 25 to about 500m² /g. The porous carrier material should be relatively refractory tothe conditions utilized in the hydrocarbon conversion process, and it isintended to include within the scope of the present invention carriermaterials which have traditionally been utilized in dual-functionhydrocarbon conversion catalysts such as: (1) activated carbon, coke orcharcoal; (2) silica or silica gel, silicon carbide, clays, andsilicates including those synthetically prepared and naturallyoccurring, which may or may not be acid treated for example, attapulgusclay, china clay, diatomaceous earth, fuller's earth, kaolin,kieselguhr, etc.; (3) ceramics, porcelain, crushed firebrick, bauxite;(4) refractory inorganic oxides such as alumina, titanium dioxide,zirconium dioxide, chromium oxide, beryllium oxide, vanadium oxide,cesium oxide, hafnium oxide, zinc oxide, magnesia, boria, thoria,silica-alumina, silica-magnesia, chromia-alumina, alumina-boria,silica-zirconia, etc.; (5) crystalline zeolitic aluminosilicates such asnaturally occurring or synthetically prepared mordenite and/orfaujasite, either in the hydrogen form or in a form which has beentreated with multivalent cations; (6) spinels such as MgAl₂ O₄, FeAl₂O₄, ZnAl₂ O₄, MnAl₂ O₄, CaAl₂ O₄, and other like compounds having theformula MO.Al₂ O₃ where M is a metal having a valence of 2; and (7)combinations of elements from one or more of these groups. The preferredporous carrier materials for use in the present invention are refractoryinorganic oxides, with best results obtained with an alumina carriermaterial. Suitable alumina materials are the crystalline aluminas knownas gamma-, eta-, and theta-alumina, with gamma- or eta-alumina givingbest results. In addition, in some embodiments the alumina carriermaterial may contain minor proportions of other well known refractoryinorganic oxides such as silica, zirconia, magnesia, etc.; however, thepreferred support is substantially pure gamma- or eta-alumina. Preferredcarrier materials have an apparent bulk density of about 0.3 to about0.8 g/cc and surface area characteristics such that the average porediameter is about 20 to 300 Angstroms, the pore volume (B.E.T.) is about0.1 to about 1 cc/g and the surface area (B.E.T.) is about 100 to about500 m² /g. In general, best results are typically obtained with agamma-alumina carrier material which is used in the form of sphericalparticles having: a relatively small diameter (i.e. typically about 1/16inch), an apparent bulk density of about 0.3 to about 0.8 g/cc, a porevolume (B.E.T.) of about 0.3 to about 0.8 cc/g, and a surface area(B.E.T.) of about 100 to about 250 m² /g.

The preferred alumina carrier material may be prepared in any suitablemanner and may be synthetically prepared or naturally occurring.Whatever type of alumina is employed, it may be activated prior to useby one or more treatments including drying, calcination, steaming, etc.,and it may be in a form known as activated alumina, activated alumina ofcommerce, porous alumina, alumina gel, etc. For example, the aluminacarrier may be prepared by adding a suitable alkaline reagent, such asammonium hydroxide, to a salt of aluminum such as aluminum chloride,aluminum nitrate, etc., in an amount to form an aluminum hydroxide gelwhich upon drying and calcining is converted to alumina. The aluminacarrier may be formed in any desired shape such as spheres, pills,cakes, extrudates, powders, granules, tablets, etc., and utilized in anydesired size. For the purpose of the present invention a particularlypreferred form of alumina is the sphere, and alumina spheres may becontinuously manufactured by the well-known oil drop method whichcomprises: forming an alumina hydrosol by any of the techniques taughtin the art and preferably by reacting aluminum metal with hydrochloricacid, combining the resultant hydrosol with a suitable gelling agent anddropping the resultant mixture into an oil bath maintained at elevatedtemperatures. The droplets of the mixture remain in the oil bath untilthey set and form hydrogel spheres. The spheres are then continuouslywithdrawn from the oil bath and typically subjected to specific agingtreatments in oil and an ammoniacal solution to further improve theirphysical characteristics. The resulting aged and gelled particles arethen washed and dried at a relatively low temperature of about 300° F.to about 400° F. and subjected to a calcination procedure at atemperature of about 850° F. to about 1300° F. for a period of about 1to about 20 hours. This treatment effects conversion of the aluminahydrogel to the corresponding crystalline gamma-alumina. See theteachings of U.S. Pat. No. 2,620,314 for additional details.

Another particularly preferred alumina carrier material is synthesizedfrom a unique crystalline alumina powder which has been characterized inU.S. Pat. Nos. 3,852,190 and 4,012,313 as a by-product from a Zieglerhigher alcohol synthesis reaction as described in Ziegler's U.S. Pat.No. 2,892,858. For purposes of simplification, the name "Ziegleralumina" is used herein to identify this material. It is presentlyavailable from the Conoco Chemical Division of Continental Oil Companyunder the trademark Catapal. This material is an extremely high purityalpha-alumina monohydrate (boehmite) which after calcination at a hightemperature has been shown to yield a high purity gamma-alumina. It iscommercially available in three forms: (1) Catapal SB--a spray driedpowder having a typical surface area of 250 m² /g; (2) Catapal NG--arotary kiln dried alumina having a typical surface area of 180 m² /g;and (3) Dispal M--a finely divided dispersable product having a typicalsurface area of about 185 m² /g. For purposes of the present invention,the preferred starting material is the spray dried powder, Catapal SB.This alpha-alumina monohydrate powder may be formed into a suitablecatalyst material according to any of the techniques known to thoseskilled in the catalyst carrier material forming art. Spherical carriermaterial particles can be formed, for example, from this Ziegler aluminaby: (1) converting the alpha-alumina monohydrate powder into an aluminasol by reaction with a suitable peptizing acid and water and thereafterdropping a mixture of the resulting sol and a gelling agent into an oilbath to form spherical particles of an alumina gel which are easilyconverted to a gamma-alumina carrier material by known methods; (2)forming an extrudate from the powder by established methods andthereafter rolling the extrudate particles on a spinning disc untilspherical particles are formed which can then be dried and calcined toform the desired particles of spherical carrier material; and (3)wetting the powder with a suitable peptizing agent and thereafterrolling particles of the powder into spherical masses of the desiredsize in much the same way that children have been known to make parts ofsnowmen by rolling snowballs down hills covered with wet snow. Thisalumina powder can also be formed in any other desired shape or type ofcarrier material known to those skilled in the art such as rods, pills,pellets, tablets, granules, extrudates and the like forms by methodswell known to the practitioners of the catalyst carrier material formingart. The preferred type of carrier material for the present invention isa cylindrical extrudate having a diameter of about 1/32" to about 150 "(especially about 1/16") and a length to diameter (L/D) ratio of about1:1 to about 5:1, with a L/D ratio of about 2:1 being especiallypreferred. The especially preferred extrudate form of the carriermaterial is preferably prepared by mixing the alumina powder with waterand a suitable peptizing agent such as nitric acid, acetic acid,aluminum nitrate and the like material until an extrudable dough isformed. The amount of water added to form the dough is typicallysufficient to give a loss on ignition (LOI) at 500° C. of about 45 to 65wt. %, with a value of about 55 wt. % being especially preferred. On theother hand, the acid addition rate is generally sufficient to provideabout 2 to 7 wt. % of the volatile free alumina powder used in the mix,with a value of about 3 to 4% being especially preferred. The resultingdough is then extruded through a suitably sized die to form extrudateparticles. It is to be noted that it is within the scope of the presentinvention to treat the resulting dough with an aqueous solution ofammonium hydroxide in accordance with the teachings of U.S. Pat. No.3,661,805. This treatment may be performed either before or afterextrusion, with the former being preferred. These particles are thendried at a temperature of about 500° F. to 800° F. for a period of about0.1 to about 5 hours and thereafter calcined at a temperature of about900° F. to about 1500° F. for a period of about 0.5 to about 5 hours toform the preferred extrudate particles of the Ziegler alumina carriermaterial. In addition, in some embodiments of the present invention theZiegler alumina carrier material may contain minor proportions of otherwell known refractory inorganic oxides such as silica, titanium dioxide,zirconium dioxide, chromium oxide, beryllium oxide, vanadium oxide,cesium oxide, hafnium oxide, zinc oxide, iron oxide, cobalt oxide,magnesia, boria, thoria, and the like materials which can be blendedinto the extrudable dough prior to the extrusion of same. In the samemanner crystalline zeolitic aluminosilicates such as naturally occurringor synthetically prepared mordenite and/or faujasite, either in thehydrogen form or in a form which has been treated with a multivalentcation, such as a rare earth, can be incorporated into this carriermaterial by blending finely divided particles of same into theextrudable dough prior to extrusion of same. A preferred carriermaterial of this type is substantially pure Ziegler alumina having anapparent bulk density (ABD) of about 0.6 to 1 g/cc (especially an ABD ofabout 0.7 to about 0.85 g/cc), a surface area of about 150 to about 280m² /g (preferably about 185 to about 235 m² /g), and a pore volume ofabout 0.3 to about 0.8 cc/g.

A second essential ingredient of the subject catalyst is the platinumgroup component. That is, it is intended to cover the use of platinum,iridium, osmium, ruthenium, rhodium, palladium, or mixtures thereof, asa second component of the present composite. It is an essential featureof the present invention that substantially all of this platinum groupcomponent exists within the final catalytic composite in the elementalmetallic state. Generally, the amount of this component present in thefinal catalytic composite is small compared to the quantities of theother components combined therewith. In fact, the platinum groupcomponent generally will comprise about 0.01 to about 2 wt. % of thefinal catalytic composite, calculated on an elemental basis. Excellentresults are obtained when the catalyst contains about 0.05 to about 1wt. % of platinum, iridium, rhodium, or palladium metal. Particularlypreferred mixtures of these metals are platinum and iridium, andplatinum and rhodium.

This platinum group component may be incorporated in the catalyticcomposite in any suitable manner known to result in a relatively uniformdistribution of this component in the carrier material such ascoprecipitation or cogelation, ion exchange or impregnation. Thepreferred method of preparing the catalyst involves the utilization of asoluble, decomposable compound of platinum group metal to impregnate thecarrier material in a relatively uniform manner. For example, thiscomponent may be added to the support by commingling the latter with anaqueous solution of chloroplatinic or chloroiridic or chloropalladicacid. Other water-soluble compounds or complexes of platinum groupmetals may be employed in impregnation solutions and include ammoniumchloroplatinate, bromoplatinic acid, platinum trichloride, platinumtetrachloride hydrate, platinum dichlorocarbonyl dichloride,dinitrodiaminoplatinum, sodium tetranitroplatinate (II), palladiumchloride, palladium nitrate, palladium sulfate, diamminepalladium (II)hydroxide, tetramminepalladium (II) chloride, hexamminerhodium chloride,rhodium carbonylchloride, rhodium trichloride hydrate, rhodium nitrate,sodium hexachlororhodate (III), sodium hexanitrorhodate (III), iridiumtribromide, iridium dichloride, iridium tetrachloride, sodiumhexanitroiridate (III), potassium or sodium chloroiridate, potassiumrhodium oxalate, etc. The utilization of a platinum, iridium, rhodium,or palladium chloride compound, such as chloroplatinic, chloroiridic, orchloropalladic acid or rhodium trichloride hydrate, is preferred sinceit facilitates the incorporation of both the platinum group componentsand at least a minor quantity of the halogen component in a single step.Hydrogen chloride or the like acid is also generally added to theimpregnation solution in order to further facilitate the incorporationof the halogen component and the uniform distribution of the metalliccomponents throughout the carrier material. In addition, it is generallypreferred to impregnate the carrier material after it has been calcinedin order to minimize the risk of washing away the valuable platinumgroup compounds; however, in some cases it may be advantageous toimpregnate the carrier material when it is in a gelled state.

A third essential constituent of the multimetallic catalyst of thepresent invention is a rhenium component. This component may in generalbe present in the instant catalytic composite in any catalyticallyavailable form such as the elemental metal, a compound like the oxide,hydroxide, halide, oxyhalide, sulfide, or in chemical combination withone or more of the other ingredients of the catalyst. Although it is notintended to restrict the present invention by this explanation, it isbelieved that best results are obtained when the rhenium component ispresent in the composite in a form wherein substantially all of therhenium moiety is in the elemental metallic state or in a state which isreducible to the elemental metallic state under hydrocarbondehydrocyclization conditions or in a mixture of these states. Thisrhenium component can be used in any amount which is catalyticallyeffective, with good results obtained, on an elemental basis, with about0.01 to about 5 wt. % rhenium in the catalyst. Best results areordinarily achieved with about 0.05 to about 1 wt. % rhenium, calculatedon an elemental basis, and with an atomic ratio of rhenium to platinumgroup metal of about 0.1:1 to about 10:1, especially about 0.5:1 toabout 5:1.

This rhenium component may be incorporated into the porous carriermaterial in any suitable manner known to the art to result in arelatively uniform dispersion of the rhenium moiety in the carriermaterial, such as by coprecipitation or cogelation or coextrusion withthe porous carrier material, ion exchange with the gelled carriermaterial, or impregnation of the carrier material either after, before,or during the period when it is dried and calcined. It is to be notedthat it is intended to include within the scope of the present inventionall conventional methods for incorporating and simultaneously uniformlydistributing a metallic component in a catalytic composite and theparticular method of incorporation used is not deemed to be an essentialfeature of the present invention. One acceptable method of incorporatingthe rhenium component into the porous carrier material involvescogelling or coprecipitating the rhenium component in the form of thecorresponding hydrous oxide during the preparation of the preferredcarrier material, alumina. This method typically involves the additionof a suitable sol-soluble and decomposable rhenium compound such asperrhenic acid or a salt thereof to the alumina hydrosol and thencombining the hydrosol with a suitable gelling agent and dropping theresulting mixture into an oil bath, etc., as explained in detailhereinbefore. After drying and calcining the resulting gelled carriermaterial in air, there is obtained an intimate combination of aluminaand rhenium oxide and/or oxychloride. An especially preferred method ofincorporating the rhenium component into the porous carrier materialinvolves utilization of a soluble, decomposable compound of rhenium toimpregnate the porous carrier material. In general, the solvent used inthis impregnation step is selected on the basis of the capability todissolve the desired rhenium compound without adversely affecting thecarrier material or the other ingredients of the catalyst--for example,a suitable alcohol, ether, acid and the like solvents. The solvent ispreferably an aqueous, acidic solution. The rhenium component may beadded to the carrier material by commingling the latter with an aqueousacidic solution of suitable rhenium salt, complex, or compound such asperrhenic acid, ammonium perrhenate, sodium perrhenate, potassiumperrhenate, potassium rhenium oxychloride (K₂ ReOCl₅), potassiumhexachlororhenate (IV), rhenium chloride, rhenium heptoxide and the likecompounds. A particularly preferred impregnation solution comprises anacidic aqueous solution of perrhenic acid. Suitable acids for use in theimpregnation solution are: inorganic acids such as hydrochloric acid,nitric acid, and the like, and strongly acidic organic acids such asoxalic acid, malonic acid, citric acid, and the like. In general, therhenium component can be impregnated either prior to, simultaneouslywith, or after the platinum group component is added to the carriermaterial. However, excellent results are obtained when the rheniumcomponent is added simultaneously with the addition of the platinumgroup component.

After the platinum group and rhenium components are combined with theporous carrier material, the resulting platinum group metal- and rheniumcontaining carrier material will generally be dried at a temperature ofabout 200° F. to about 600° F. for a period of typically about 1 toabout 24 hours or more and thereafter oxidized at a temperature of about700° F. to about 1100° F. in an air or oxygen atmosphere for a period ofabout 0.5 to about 10 or more hours or converts substantially all of theplatinum group and rhenium components to the corresponding metallicoxides. To incorporate the halogen component in the present composition,best results are generally obtained when the halogen content of theplatinum group metal- and rhenium-containing carrier material isadjusted during this oxidation step by including a halogen or ahalogen-containing compound in the air or oxygen atmosphere utilized.For purposes of the present invention, the particularly preferredhalogen is chlorine and it is highly recommended that the halogencompound utilized in this halogenation step be either hydrochloric acidor a hydrochloric acid producing substance. In particular, when thehalogen component of the catalyst is chlorine, it is preferred to use amolar ratio of H₂ O to HCl of about 5:1 to about 100:1 during at least aportion of the oxidation step which follows the platinum group metalimpregnation in order to adjust the final chlorine content of thecatalyst to a range of about 0.1 to about 3.5 wt. %. Preferably, theduration of this halogenation step is about 1 to 5 or more hours.

A preferred feature of the present invention involves subjecting theresulting oxidized, platinum group metal- and rhenium-containing, andtypically halogen-treated, carrier material to a substantiallywater-free reduction step before the incorporation of the rutheniumcomponent by means of the ruthenium carbonyl reagent. The importance ofthis reduction step comes from my observation that when an attempt ismade to prepare the instant catalytic composite without first reducingthe platinum group component, no significant improvement in theplatinum-ruthenium-rhenium catalyst system is obtained; put another way,it is my finding that it is essential for the platinum group componentto be well dispersed in the porous carrier material in the elementalmetallic state prior to incorporation of the ruthenium carbonylcomponent by the unique procedure of the present invention in order forsynergistic interaction of the ruthenium carbonyl with the dispersedplatinum group metal to occur according to the theories that I havepreviously explained. Accordingly, this reduction step is designed toreduce substantially all of the platinum group component to theelemental metallic state and to assure a relatively uniform and finelydivided dispersion of this metallic component throughout the porouscarrier material. Preferably a substantially pure and dry hydrogenstream (by the use of the word "dry" I mean that it contains less than20 vol. ppm water and preferably less than 5 vol. ppm water) is used asthe reducing agent in this step. The reducing agent is contacted withthe oxidized, platinum group metal- and rhenium-containing carriermaterial at conditions including a reduction temperature of about 450°F. to about 1200° F. for a period of about 0.5 to about 10 or more hoursselected to reduce substantially all of the platinum group component tothe elemental metallic state. Once this condition of finely divideddispersed platinum group metal in the porous carrier material isachieved, it is important that environments and/or conditions that coulddisturb or change this condition be avoided; specifically, I much preferto maintain the freshly reduced carrier material containing the platinumgroup metal under a blanket of inert gas to avoid any possibility ofcontamination of same either by water or by oxygen.

A fourth essential ingredient of the present multimetallic catalyticcomposite is a special ruthenium component which I have chosen tocharacterize as a pyrolyzed ruthenium carbonyl in order to emphasizethat the ruthenium moiety of interest in my invention is the rutheniumproduced by decomposing a ruthenium carbonyl in the presence of a finelydivided dispersion of a platinum group metal and in the absence ofmaterials such as oxygen or water which could interfere with the basicdesired interaction of the ruthenium carbonyl component with theplatinum group metal component as previously explained. In view of thefact that all of the ruthenium contained in a ruthenium carbonylcompound is present in the elemental metallic state, a preferredrequirement of my invention is that the resulting reaction product ofthe ruthenium carbonyl compound or complex with the platinum groupmetal- and rhenium-loaded carrier material is not subjected toconditions which could in any way interfere with the maintenance of theruthenium moiety in the elemental metallic state; consequently,avoidance of any conditions which would tend to cause the oxidation ofany portion of the ruthenium ingredient or of the platinum groupingredient is a requirement for full realization of the synergisticinteraction enabled by the present invention. This ruthenium carbonylcomponent may be utilized in the resulting composite in any amount thatis catalytically effective with the preferred amount typicallycorresponding to about 0.01 to about 2 wt. % thereof, calculated on anelemental ruthenium basis. Best results are ordinarily obtained withabout 0.05 to about 1 wt. % ruthenium. Best results are also achievedwhen the amount of the ruthenium carbonyl component is set as a functionof the amount of the platinum group component to achieve acarbonyl-derived ruthenium to platinum group metal atomic ratio of about0.1:1 to about 5:1, with an especially useful range comprising about0.2:1 to about 3:1 and with superior results achieved at an atomic ratioof ruthenium to platinum group metal of about 0.5:1 to about 1.0:1.

The ruthenium carbonyl ingredient may be reacted with the reducedplatinum group metal- and rhenium-containing porous carrier material inany suitable manner known to those skilled in the catalyst formulationart which results in relatively good contact between the rutheniumcarbonyl complex and the platinum group component contained in theporous carrier material. One acceptable procedure for incorporating theruthenium carbonyl component into the composite involves subliming thiscomplex under conditions which enable it to pass into the vapor phasewithout being decomposed and thereafter contacting the resultingruthenium carbonyl sublimate with the platinum group metal- andrhenium-containing porous carrier material under conditions designed toachieve intimate contact of the carbonyl reagent with the platinum groupmetal dispersed on the carrier material. Typically, this procedure isperformed under vacuum at a temperature of about 70° to about 250° F.for a period of time sufficient to react the desired amount of rutheniumcarbonyl with the carrier material. In some cases an inert carrier gassuch as nitrogen can be admixed with the ruthenium carbonyl sublimate inorder to facilitate the intimate contacting of same with themetal-containing porous carrier material. A particularly preferred wayof accomplishing this reaction step is an impregnation procedure whereinmetal-containing porous carrier material is impregnated with a suitablesolution containing the desired quantity of the ruthenium carbonylcomplex. For purposes of the present invention, organic solutions arepreferred, although any suitable solution may be utilized as long as itdoes not interact with the ruthenium carbonyl and cause decomposition ofsame. Obviously the organic solution should be anhydrous in order toavoid detrimental interaction of water with the ruthenium carbonylcomplex. Suitable solvents are any of the commonly available organicsolvents such as one of the available ethers, alcohols, ketones,aldehydes, paraffins, naphthenes and aromatic hydrocarbons, for example,acetone, acetyl acetone, benzaldehyde, pentane, hexane, carbontetrachloride, methyl isopropyl ketone, benzene, n-butylether, diethylether, ethylene glycol, methyl isobutyl ketone, diisobutyl ketone andthe like organic solvents. Best results are ordinarily obtained when thesolvent is acetone; consequently, the preferred impregnation solution isruthenium carbonyl dissolved in anhydrous acetone. The rutheniumcarbonyl complex suitable for use in the present invention may be eitherthe pure ruthenium carbonyl itself (i.e. Ru(CO)₅ or Ru₃ (CO)₁₂) or asubstituted ruthenium carbonyl such as the ruthenium carbonyl halidesincluding the chlorides, bromides, and iodides and the like substitutedcarbonyl complexes. After impregnation of the carrier material with theruthenium carbonyl component, it is important that the solvent beremoved or evaporated from the catalyst prior to decomposition of theruthenium carbonyl component by means of the hereinafter describedpyrolysis step. The reason for removal of the solvent is that I believethat the presence of organic materials such as hydrocarbons orderivatives of hydrocarbons during the pyrolysis step is highlydetrimental to the synergistic interaction associated with the presentinvention. This solvent is removed by subjecting the ruthenium carbonylimpregnated carrier material to a temperature of about 100° F. to about250° F. in the presence of an inert gas or under a vacuum conditionuntil no further substantial amount of solvent is observed to come offthe impregnated material. In the preferred case where acetone is used asthe impregnation solvent, this drying of the impregnated carriermaterial typically takes about one half hour at a temperature of about225° F. under moderate vacuum conditions.

After the ruthenium carbonyl component is incorporated into theplatinum- and rhenium containing porous carrier material, the resultingcomposite is, pursuant to the present invention, subjected to pyrolysisconditions designed to decompose substantially all of the rutheniumcarbonyl material, without oxidizing either the platinum group componentor the decomposed ruthenium carbonyl component. This step is preferablyconducted in an atmosphere which is substantially inert to the rutheniumcarbonyl such as in a nitrogen or noble gas-containing atmosphere.Preferably this pyrolysis step takes place in the presence of asubstantially pure and dry hydrogen stream. It is of course within thescope of the present invention to conduct the pyrolysis step undervacuum conditions. It is much preferred to conduct this step in thesubstantial absence of free oxygen and substances that could yield freeoxygen under the conditions selected. Likewise it is clear that bestresults are obtained when this step is performed in the total absence ofwater and of hydrocarbons and other organic materials. I have obtainedbest results in pyrolyzing ruthenium carbonyl while using an anhydroushydrogen stream at pyrolysis conditions including a temperature of about300° F. to about 900° F. or more, preferably about 400° F. to about 750°F., a gas hourly space velocity of about 250 to about 1500 hr.⁻¹ for aperiod of about 0.5 to about 5 or more hours until no further evolutionof carbon monoxide is noted. After the ruthenium carbonyl component hasbeen pyrolyzed, it is a much preferred practice to maintain theresulting catalytic composite in an inert environment (i.e. a nitrogenor the like inert gas blanket) until the catalyst is loaded into areaction zone for use in the conversion of hydrocarbons.

The resulting pyrolyzed catalytic composite may, in some cases, bebeneficially subjected to a presulfiding step designed to incorporate inthe catalytic composite from about 0.01 to about 1 wt. % sulfurcalculated on an elemental basis. Preferably, this presulfidingtreatment takes place in the presence of hydrogen and a suitabledecomposable sulfur-containing compound such as hydrogen sulfide, lowermolecular weight mercaptans, organic sulfides, etc. Typically, thisprocedure comprises treating the pyrolyzed catalyst with a sulfiding gassuch as a mixture of hydrogen and hydrogen sulfide containing about 10moles of hydrogen per mole of hydrogen sulfide at conditions sufficientto effect the desired incorporation of sulfur, generally including atemperature ranging from about 50° F. up to about 1000° F. It isgenerally a preferred practice to perform this presulfiding step undersubstantially water-free and oxygen-free conditions. It is within thescope of the present invention to maintain or achieve the sulfided stateof the present catalyst during use in the conversion of hydrocarbons bycontinuously or periodically adding a decomposable sulfur-containingcompound, selected from the above mentioned list, to the reactorcontaining the activated and attenuated catalyst in an amount sufficientto provide about 1 to 500 wt. ppm, preferably about 1 to about 20 wt.ppm of sulfur, based on hydrocarbon charge. According to another mode ofoperation, this sulfiding step may be accomplished during the pyrolysisstep by utilizing a ruthenium carbonyl reagent which has asulfur-containing ligand or by adding H₂ S to the hydrogen stream whichis preferably used therein.

It is essential to incorporate a halogen component into the acidicmultimetallic catalytic composite used in the present invention.Although the precise form of the chemistry of the association of thehalogen component with the carrier material is not entirely known, it iscustomary in the art to refer to the halogen component as being combinedwith the carrier material, or with the other ingredients of the catalystin the form of the halide (e.g. as the chloride). This combined halogenmay be either fluorine, chlorine, iodine, bromine, or mixtures thereof.Of these, fluorine and, particularly, chlorine are preferred for thepurposes of the present invention. The halogen may be added to thecarrier material in any suitable manner, either during preparation ofthe support or before or after the addition of the other components. Forexample, the halogen may be added, at any stage of the preparation ofthe carrier material or to the calcined carrier material, as an aqueoussolution of a suitable, decomposable halogen-containing compound such ashydrogen fluoride, hydrogen chloride, hydrogen bromide, ammoniumchloride, etc. The halogen component or a portion thereof, may becombined with the carrier material during incorporation of the latterwith the platinum group, ruthenium, or rhenium components; for example,through the utilization of a mixture of chloroplatinic acid and hydrogenchloride. In another situation, the alumina hydrosol which is typicallyutilized to form the preferred alumina carrier material may containhalogen and thus contribute at least a portion of the halogen componentto the final composite. For the dehydrocyclization reaction, the halogenwill be typically combined with the carrier material in an amountsufficient to result in a final composite that contains about 0.1 toabout 3.5%, and preferably about 0.5 to about 1.5%, by weight ofhalogen, calculated on an elemental basis. It is to be understood thatthe specified level of halogen component in the instant catalyst can beachieved or maintained during use in the dehydrocyclization ofhydrocarbons by continuously or periodically adding to the reaction zonea decomposable halogen-containing compound such as an organic chloride(e.g. ethylene dichloride, carbon tetrachloride, t-butyl chloride) in anamount of about 1 to 100 wt. ppm of the hydrocarbon feed, andpreferably, about 1 to 10 wt. ppm.

Regarding especially preferred amounts of the various metalliccomponents of the subject catalyst, I have found it to be an excellentpractice to specify the amounts of the ruthenium component and therhenium component as a function of the amount of the platinum groupcomponent. On this basis, the amount of the ruthenium component isordinarily selected so that the atomic ratio of ruthenium to platinumgroup metal contained in the composite is about 0.1:1 to about 5:1, withthe preferred range being about 0.2:1 to about 3:1. Similarly, theamount of the rhenium component is ordinarily selected to produce acomposite containing an atomic ratio of rhenium to platinum group metalof about 0.1:1 to about 10:1, with the preferred range being about 0.5:1to about 5:1.

Regardless of the details of how the components of the catalyst arecombined with the porous carrier material, the final catalyst generallywill be dried at a temperature of about 200° F. to about 600° F. for aperiod of at least about 1 to about 24 hours or more, and finallycalcined or oxidized at a temperature of about 700° F. to about 1100° F.in an air to oxygen atmosphere for a period of about 0.5 to about 10hours in order to convert substantially all of the metallic componentsto the corresponding oxide form. Because a halogen component is utilizedin the catalyst, best results are generally obtained when the halogencontent of the catalyst is adjusted during at least a portion of thisoxidation step by including a halogen or a halogen-containing compoundsuch as HCl or an HCl-producing substance in the air or oxygenatmosphere utilized. In particular, when the halogen component of thecatalyst is chlorine, it is preferred to use a mole ratio of H₂ O to HClof about 5:1 to about 100:1 during at least a portion of the oxidationstep in order to adjust the final chlorine content of the catalyst to arange of about 0.1 to about 3.5 wt. %. Preferably, the duration of thishalogenation step is about 1 to 5 hours.

The resultant oxidized catalytic composite is preferably subjected to asubstantially water-free reduction step prior to its use in thedehydrocyclization of hydrocarbons. This step is designed to reduce theplatinum group component to the elemental metallic state. Preferably, asubstantially pure and dry hydrogen stream (i.e. less than 20 vol. ppmH₂ O) is used as the reducing agent in this step. The reducing agent iscontacted with the oxidized catalyst at conditions including a reductiontemperature of about 400° F. to about 1200° F. and a period of time ofabout 0.5 to 10 hours effective to reduce substantially all of theplatinum group component to the elemental metallic state. This reductiontreatment may be performed in situ as part of a start-up sequence ifprecautions are taken to pre-dry the plant to a substantially water-freestate and if a substantially water-free hydrogen stream is used.

According to the present invention, the dehydrocyclizable hydrocarbon iscontacted with the instant acidic multimetallic catalyst in adehydrocyclization zone maintained at dehydrocyclization conditions.This contacting may be accomplished by using the catalyst in a fixed bedsystem, a moving bed system, a fluidized bed system, or in a batch typeoperation; however, in view of the danger of attrition losses of thevaluable catalyst and of well-known operational advantages, it ispreferred to use either a fixed bed system or a dense-phase moving bedsystem such as is shown in U.S. Pat. No. 3,725,249. It is alsocontemplated that the contacting step can be performed in the presenceof a physical mixture of particles of the catalyst of the presentinvention and particles of a conventional dual-function catalyst of theprior art. In a fixed bed system, the dehydrocyclizablehydrocarbon-containing charge stock is preheated by any suitable heatingmeans to the desired reaction temperature and then passed into adehydrocyclization zone containing a fixed bed of the acidicmultimetallic catalyst. It is, of course, understood that thedehydrocyclization zone may be one or more separate reactors withsuitable means therebetween to ensure that the desired conversiontemperature is maintained at the entrance to each reactor. It is alsoimportant to note that the reactants may be contacted with the catalystbed in either upward, downward, or radial flow fashion with the latterbeing preferred. In addition, the reactants may be in the liquid phase,a mixed liquid-vapor phase, or a vapor phase when they contact thecatalyst, with best results obtained in the vapor phase. Thedehydrocyclization system then preferably comprises a dehydrocyclizationzone containing one or more fixed beds or dense-phase moving beds of theinstant catalyst. In a multiple bed system, it is, of course, within thescope of the present invention to use the present catalyst in less thanall of the beds with a conventional dual-function catalyst being used inthe remainder of the beds. This dehydrocyclization zone may be one ormore separate reactors with suitable heating means therebetween tocompensate for the endothermic nature of the dehydrocyclization reactionthat takes place in each catalyst bed.

Although hydrogen is the preferred diluent for use in the subjectdehydrocyclization method, in some cases other art-recognized diluentsmay be advantageously utilized, either individually or in admixture withhydrogen, such as C₁ to C₅ paraffins such as methane, ethane, propane,butane and pentane; carbon dioxide, the like diluents, and mixturesthereof. Hydrogen is preferred because it serves the dual-function ofnot only lowering the partial pressure of the dehydrocyclizablehydrocarbon, but also of suppressing the formation ofhydrogen-deficient, carbonaceous deposits (commonly called coke) on thecatalytic composite. Ordinarily, hydrogen is utilized in amountssufficient to insure a hydrogen to hydrocarbon mole ratio of about 0.1:1to about 10:1, with best results obtained in the range of about 0.5:1 toabout 5:1. The hydrogen stream charged to the dehydrocyclization zonewill typically be recycled hydrogen obtained from the effluent streamfrom this zone after a suitable hydrogen separation step.

In the case where the sulfur content of the charge stock for the presentprocess is greater than about 100 wt. ppm, it may be necessary to treatthe charge stock in order to remove the undesired sulfur contaminantstherefrom. This is easily accomplished by using any one of theconventional catalytic pretreatment methods such as hydrorefining,hydrotreating, hydrodesulfurization and the like to remove substantiallyall sulfurous, nitrogenous, and water-yielding contaminants from thisfeed stream. Ordinarily this involves subjecting the sulfur-containingfeed stream to contact with a suitable sulfur-resistant hydrorefiningcatalyst in the presence of hydrogen under conversion conditionsselected to decompose sulfur contaminants contained therein and formhydrogen sulfide. The hydrorefining catalyst typically comprises one ormore of the oxides or sulfides of the transition metals of Groups VI andVIII of the Periodic Table. A particularly preferred hydrorefiningcatalyst comprises a combination of a metallic component from the irongroup metals of Group VIII and of a metallic component of the Group VItransition metals combined with a suitable porous refractory support.Particularly good results have been obtained when the iron groupcomponent is cobalt and/or nickel and the Group VI transition metal ismolybdenum or tungsten. The preferred support for this type of catalystis a refractory inorganic oxide of the type previously mentioned. Forexample, good results are obtained with a hydrorefining catalystcomprising cobalt oxide and molybdenum oxide supported on a carriermaterial comprising alumina and silica. The conditions utilized in thishydrorefining step are ordinarily selected from the following ranges: atemperature of about 600° to about 950° F., a pressure of about 500 toabout 5000 psig., a liquid hourly space velocity of about 1 to about 20hr.⁻¹, and a hydrogen circulation rate of about 500 to about 10,000standard cubic feet of hydrogen per barrel of charge. After thishydrorefining step, the hydrogen sulfide, ammonia, and water liberatedtherein, are then easily removed from the resulting purified chargestock by conventional means such as a suitable stripping operation.Specific hydrorefining conditions are selected from the ranges givenabove as a function of the amounts and kinds of the sulfur contaminantsin the feed stream in order to produce a substantially sulfur-freecharge stock which is then charged to the process of the presentinvention.

It is also generally preferred to utilize the novel acidic multimetalliccatalytic composite in a substantially water-free environment. Essentialto the achievement of this condition in the dehydrocyclization zone isthe control of the water level present in the charge stock and thediluent stream which is being charged to the zone. Best results areordinarily obtained when the total amount of water entering theconversion zone from any source is held to a level less than 20 ppm. andpreferably less than 5 ppm. expressed as weight of equivalent water inthe charge stock. In general, this can be accomplished by carefulcontrol of the water present in the charge stock and in the diluentstream. The charge stock can be dried by using any suitable drying meansknown to the art, such as a conventional solid adsorbent having a highselectivity for water, for instance, sodium or calcium crystallinealuminosilicates, silica gel, activated alumina, molecular sieves,anhydrous calcium sulfate, high surface area sodium, and the likeadsorbents. Similarly, the water content of the charge stock may beadjusted by suitable stripping operations in a fractionation column orlike device. And in some cases, a combination of adsorbent drying anddistillation drying may be used advantageously to effect almost completeremoval of water from the charge stock. In an especially preferred modeof operation, the charge stock is dried to a level corresponding to lessthan 5 wt. ppm. of H₂ O equivalent. In general, it is preferred tomaintain the diluent stream entering the hydrocarbon conversion zone ata level of about 10 vol. ppm. of water or less and most preferably about5 vol. ppm. or less. If the water level in the diluent stream is toohigh, drying of same can be conveniently accomplished by contacting thisstream with a suitable desiccant such as those mentioned above.

The dehydrocyclization conditions used in the present method include areactor pressure which is selected from the range of about 0 psig. toabout 250 psig., with the preferred pressure being about 50 psig. toabout 150 psig. In fact, it is a singular advantage of the presentinvention that it allows stable operation at lower pressure than haveheretofore been successfully utilized in dehydrocyclization system withall platinum monometallic catalysts. In other words, the acidicmultimetallic catalyst of the present invention allows the operation ofa dehydrocyclization system to be conducted at lower pressure for aboutthe same or better catalyst cycle life before regeneration as has beenheretofore realized with conventional monometallic catalysts at higherpressure.

The temperature required for dehydrocyclization with the instantcatalyst is markedly lower than that required for a similar operationusing a high quality catalyst of the prior art. This significant anddesirable feature of the present invention is a consequence of theextraordinary activity of the acidic multimetallic catalyst of thepresent invention for the dehydrocyclization reaction. Hence, thepresent invention requires a temperature in the range of from about 800°F. to about 1100° F. and preferably about 850° F. to about 1000° F. Asis well known to those skilled in the dehydrocyclization art, theinitial selection of the temperature within this broad range is madeprimarily as a function of the desired conversion level of thedehydrocyclizable hydrocarbon considering the characteristics of thecharge stock and of the catalyst. Ordinarily, the temperature then isthereafter slowly increased during the run to compensate for theinevitable deactivation that occurs to provide a relatively constantvalue for conversion. Therefore, it is a feature of the presentinvention that not only is the initial temperature requirementsubstantially lower, but also the rate at which the temperature isincreased in order to maintain a constant conversion level issubstantially lower for the catalyst of the present invention than foran equivalent operation with a high quality dehydrocyclization catalystwhich is manufactured in exactly the same manner as the catalyst of thepresent invention except for the inclusion of the ruthenium and rheniumcomponents. Moreover, for the catalyst of the present invention, thearomatic yield loss for a given temperature increase is substantiallylower than for a high quality dehydrocyclization catalyst of the priorart.

The liquid hourly space velocity (LHSV) used in the instantdehydrocyclization method is selected from the range of about 0.1 toabout 5 hr.⁻¹, with a value in the range of about 0.3 to about 2 hr.⁻¹being preferred. In fact, it is a feature of the present invention thatit allows operations to be conducted at higher LHSV than normally can bestably achieved in a dehydrocyclization process with a high qualitydehydrocyclization catalyst of the prior art. This last feature is ofimmense economic significance because it allows a dehydrocyclizationprocess to operate at the same throughput level with less catalystinventory or at greatly increased throughput level with the samecatalyst inventory than that heretofore used with conventionaldehydrocyclization catalysts at no sacrifice in catalyst life beforeregeneration.

The following illustrative embodiments are given to describe further thepreparation of the acidic multimetallic catalyst composite used in thepresent invention and the beneficial use thereof in thedehydrocyclization of hydrocarbons. It is understood that theembodiments are intended to be illustrative rather than restrictive.

These embodiments are all to be performed in a laboratory scaledehydrocyclization plant comprising a reactor, a hydrogen separatingzone, heating means, cooling means, pumping means, compressing means,and the like conventional equipment. In this plant, a sulfur-free feedstream containing the dehydrocyclizable hydrocarbon is combined with ahydrogen recycle stream and the resultant mixture heated to the desiredconversion temperature, which refers herein to the temperaturemaintained at the inlet to the reactor. The heated mixture is thenpassed into contact with the instant acidic multimetallic catalyst whichis maintained in a sulfur-free and water-free environment and which ispresent as a fixed bed of catalyst particles in the reactor. Thepressures reported herein are recorded at the outlet from the reactor.An effluent stream is withdrawn from the reactor, cooled, and passedinto the hydrogen-separating zone wherein a hydrogen-containing gasphase separates from a hydrocarbon-rich liquid phase containing aromatichydrocarbons, unconverted dehydrocyclizable hydrocarbons, andby-products of the dehydrocyclization reaction. A portion of thehydrogen-containing gas phase is recovered as excess recycle gas and theremaining portion is passed through a high surface area sodium scrubberand the resulting substantially water-free and sulfur-free hydrogenstream is recycled through suitable compressing means to the heatingzone as described above. The hydrocarbon-rich liquid phase from theseparating zone is withdrawn therefrom and subjected to analysis todetermine conversion and selectivity for the desired aromatichydrocarbon as will be indicated in the examples. Conversion numbers ofthe dehydrocyclizable hydrocarbon reported herein are all calculated onthe basis of disappearance of the dehydrocyclizable hydrocarbon and areexpressed in weight percent. Similarly, selectivity numbers are reportedon the basis of weight of desired aromatic hydrocarbon produced per 100weight parts of dehydrocyclizable hydrocarbon charged.

All of the catalysts to be utilized in these examples are preparedaccording to the following general method with suitable modification instoichiometry to achieve the compositions reported in each example.

A sulfur-free alumina carrier material comprising 1/16 inch spheres wasprepared by: forming an aluminum hydroxy chloride sol by dissolvingsubstantially pure aluminum pellets in a hydrochloric acid solution,adding hexamethylenetetramine to the resulting alumina sol, gelling theresulting solution by dropping it into an oil bath to form sphericalparticles of an alumina hydrogel, aging and washing the resultingparticles and finally drying and calcining the aged and washed particlesto form spherical particles of gamma-alumina containing on an elementalbasis, about 0.3 wt. % combined chlorine. Additional details as to thismethod of preparing the preferred gamma-alumina carrier material aregiven in the teachings of U.S. Pat. No. 2,620,314.

An aqueous impregnation solution containing chloroplatinic acid,perrhenic acid and hydrogen chloride was then prepared. The aluminacarrier material particles were thereafter admixed with thisimpregnation solution. The amounts of the metallic reagents contained inthis impregnation solution were calculated to result in a finalcomposite containing, on an elemental basis, about 0.375 wt. % platinumand about 0.25 wt. % rhenium. In order to insure uniform dispersion ofthe platinum component throughout the carrier material, the amount ofhydrogen chloride used in this impregnation solution was about 2 wt. %of the alumina particles. This impregnation step was performed by addingthe carrier material particles to the impregnation mixture with constantagitation. In addition, the volume of the solution was approximately thesame as the bulk volume of the alumina carrier material particles sothat all of the particles were immersed in the impregnation solution.The impregnation mixture was maintained in contact with the carriermaterial particles for a period of about 1/2 to about 3 hours at atemperature of about 70° F. Thereafter, the temperature of theimpregnation mixture was raised to about 225° F. and the excess solutionwas evaporated in a period of about 1 hour. The resulting driedimpregnated particles were then subjected to an oxidation treatment in adry air stream at a temperature of about 975° F. and a GHSV of about 500hr.⁻¹ for about 1/2 hour. This oxidation step was designed to convertsubstantially all of the platinum ingredient to the correspondingplatinum oxide form. The resulting oxidized spheres were subsequentlycontacted in a halogen treating step with an air stream containing H₂ Oand HCl in a mole ratio of about 30:1 for about 2 hours at 975° F. and aGHSV of about 500 hr.⁻¹ in order to adjust the halogen content of thecatalyst particles to a value of about 1 wt. %. The halogen-treatedspheres were thereafter subjected to a second oxidation step with a dryair stream at 975° F. and a GHSV of 500 hr.⁻¹ for an additional periodof about 1/2 hour.

The resulting oxidized, halogen-treated, platinum- andrhenium-containing carrier material particles were then subjected to adry reduction treatment designed to reduce substantially all of theplatinum component to the elemental state and to maintain a uniformdispersion of this component in the carrier material. This reductionstep was accomplished by contacting the particles with ahydrocarbon-free, dry hydrogen stream containing less than 5 vol. ppm H₂O at a temperature of about 1050° F., a pressure slightly aboveatmospheric, a flow rate of hydrogen through the particles correspondingto a GHSV of about 400 hr.⁻¹ and for a period of about one hour.

Ruthenium carbonyl complex, Ru₃ (CO)₁₂, was thereafter dissolved in ananhydrous acetone solvent in order to prepare the ruthenium carbonylsolution which was used as the vehicle for reacting ruthenium carbonylwith the carrier material containing the uniformly dispersed platinumand rhenium. The amount of this complex used was selected to result in afinished catalyst containing about 0.1 wt. % ruthenium derived fromruthenium carbonyl. The resulting ruthenium carbonyl-containing solutionwas then contacted under appropriate impregnation conditions with thereduced platinum- and rhenium-containing alumina carrier materialresulting from the previously described reduction step. The impregnationconditions utilized were: a contact time of about one half to aboutthree hours, a temperature of about 70° F. and a pressure of aboutatmospheric. It is important to note that this impregnation step wasconducted under a nitrogen blanket so that oxygen was excluded from theenvironment and also this step was performed under anhydrous conditions.Thereafter the acetone solvent was removed under flowing nitrogen at atemperature of about 175° F. for a period of about one hour. Theresulting dry ruthenium carbonyl impregnated particles were thensubjected to a pyrolysis step designed to decompose the rutheniumcarbonyl components. This step involved subjecting the rutheniumcarbonyl impregnated particles to a flowing hydrogen stream at a firsttemperature of about 230° F. for about one half hour at a GHSV of about600 hr.⁻¹ and at atmospheric pressure. Thereafter in the second portionof the pyrolysis step the temperature of the impregnated particles wasraised to about 575° F. for an additional interval of about one houruntil the evolution of CO was no longer evident.

The resulting pyrolyzed catalytic composite was then maintained under anitrogen blanket and cooled to a temperature of about 70° F. Thesecatalyst particles were then loaded under a nitrogen blanket into a mildagitation device designed to slowly roll the catalyst particles so as toprovide good contact between these particles and their gaseousenvironment. The agitation device was fitted with an inlet meansdesigned to allow fixed quantities of H₂ S to be periodically injectedinto the gaseous environment contained therein. Initially this gaseousenvironment was of course pure nitrogen. The amount of H₂ S necessary tosulfide the catalyst to a level of about 600 wt. ppm was thencalculated. The necessary amount of H₂ S was then divided into fiveportions which were then separately added via the inlet means to theagitation device at 15 minute intervals. The conditions utilized duringthis sulfiding step were: a temperature of about 70° F., a pressure ofabout atmospheric and a contact time of sulfiding agent with thecatalyst particles of about 1 and 1/4 hours. The resulting sulfidedcatalyst was then maintained under a nitrogen blanket until it wasloaded into the reactor in the subsequently described reforming test.

EXAMPLE 1

The reactor is loaded with 100 cc of an acidic catalyst containing, onan elemental basis, 0.375 wt. % platinum, 0.1 wt. % ruthenium, 0.25 wt.% rhenium, and about 1 wt. % chloride. This corresponds to an atomicratio of ruthenium to platinum of 0.5:1 and of rhenium to platinum of0.7:1. The feed stream utilized is commercial grade n-hexane. The feedstream is contacted with the catalyst at a temperature of 920° F., apressure of 125 psig, a liquid hourly space velocity of 0.75 hr.⁻¹, anda hydrogen to hydrocarbon mole ratio of 4:1. The dehydrocyclizationplant is lined-out at these conditions and a 20 hour test periodcommenced. The hydrocarbon product stream from the plant is continuouslyanalyzed by GLC (gas liquid chromatography) and about a 90% conversionof n-hexane is observed with a selectivity for benzene of about 25%.

EXAMPLE II

The acidic catalyst contains, on an elemental basis, 0.375 wt. %platinum, 0.2 wt. % ruthenium, 0.25 wt. % rhenium and about 1 wt. %combined chloride. For this catalyst, the pertinent atomic ratios are:ruthenium to platinum=1:1, and rhenium to platinum=0.7:1. The feedstream is commercial grade normal heptane. The dehydrocyclizationreactor is operated at a temperature of 900° F., a pressure of 125 psig,a liquid hourly space velocity of 0.75 hr.⁻¹, and a hydrogen gas tohydrocarbon mole ratio of 5:1. After a line-out period, a 20 hour testperiod is performed during which the average conversion of the n-heptaneis maintained at about 95% with a selectivity for aromatics (a mixtureof toluene and benzene) of about 45%.

EXAMPLE III

The acidic catalyst is the same as utilized in Example II. The feedstream is normal octane. The conditions utilized are a temperature of880° F., a pressure of 125 psig, a liquid hourly space velocity of 0.75hr.⁻¹, and a hydrogen gas to hydrocarbon mole ratio of 4:1. After aline-out period, a 20 hour test shows an average conversion of about100% and a selectivity for aromatics of about 50%.

EXAMPLE IV

The acidic catalyst contains, on an elemental basis, 0.375 wt. %platinum, 0.1 wt. % ruthenium, 0.4 wt. % rhenium and about 1 wt. %combined chloride. On an atomic basis, the ratio of ruthenium toplatinum is 0.5:1 and the ratio of rhenium to platinum is 1.12:1. Thefeed stream is a 50/50 mixture of n-hexane and n-heptane. The conditionsutilized are a temperature of 945° F., a pressure of 125 psig, a liquidhourly space velocity of 0.75 hr.⁻¹, and a hydrogen gas to hydrocarbonmole ratio of 5:1. After a line-out period, a 20 hour test is performedwith a conversion of about 100% and a selectivity for aromatics of about45%. The selectivity for benzene and toluene are about 20% and 25%,respectively.

It is intended to cover by the following claims, all changes andmodifications of the above disclosure of the present invention whichwould be self-evident to a man of ordinary skill in thecatalyst-formulation art or in the hydrocarbon dehydrocyclization art.

I claim as my invention:
 1. A method for dehydrocyclizing adehydrocyclizable hydrocarbon comprising contacting the hydrocarbon, athydrocarbon dehydrocyclization conditions, with an acidic catalyticcomposite comprising a combination of a catalytically effective amountof a pyrolyzed ruthenium carbonyl component with a porous carriermaterial containing a uniform dispersion of a catalytically effectiveamount of a platinum group component maintained in the elementalmetallic state during the incorporation and pyrolysis of the rutheniumcarbonyl component, a rhenium component and a halogen component.
 2. Amethod as defined in claim 1 wherein the dehydrocyclizable hydrocarbonis admixed with hydrogen when it contacts the catalytic composite.
 3. Amethod as defined in claim 1 wherein the platinum group component isplatinum.
 4. A method as defined in claim 1 wherein the platinum groupcomponent is iridium.
 5. A method as defined in claim 1 wherein theplatinum group component is rhodium.
 6. A method as defined in claim 1wherein the platinum group component is palladium.
 7. A method asdefined in claim 1 wherein the catalytic composite contains thecomponents in amounts, calculated on an elemental basis, correspondingto about 0.1 to about 2 wt. % ruthenium, about 0.1 to about 2 wt. %platinum group component, about 0.1 to about 5 wt. % rhenium and about0.1 to about 3.5 wt. % halogen.
 8. A method as defined in claim 1wherein the porous carrier material is a refractory inorganic oxide. 9.A method as defined in claim 7 wherein the refractory inorganic oxide isalumina.
 10. A method as defined in claim 1 wherein the halogen ischlorine.
 11. A method as defined in claim 1 wherein thedehydrocyclizable hydrocarbon is an aliphatic hydrocarbon containing 6to 20 carbon atoms per molecule.
 12. A method as defined in claim 10wherein the aliphatic hydrocarbon is an olefin.
 13. A method as definedin claim 10 wherein the aliphatic hydrocarbon is a paraffin.
 14. Amethod as defined in claim 12 wherein the paraffin hydrocarbon is aparaffin containing 6 to 10 carbon atoms per molecule.
 15. A method asdefined in claim 12 wherein the paraffin is hexane.
 16. A method asdefined in claim 12 wherein the paraffin is heptane.
 17. A method asdefined in claim 12 wherein the paraffin is octane.
 18. A method asdefined in claim 12 wherein the paraffin is nonane.
 19. A method asdefined in claim 12 wherein the paraffin is a mixture of C₆ to C₉paraffins.
 20. A method as defined in claim 1 wherein thedehydrocyclizable hydrocarbon is contained in a naphtha fraction boilingin the range of about 140° F. to about 400° F.
 21. A method as definedin claim 2 wherein the hydrocarbon dehydrocyclization conditions includea temperature of about 800° F. to about 1100° F., a pressure of about 0psig to 250 psig, an LHSV of about 0.1 to about 5 hr.⁻¹, and a hydrogento hydrocarbon mole ratio of about 0.1:1 to about 10:1.
 22. A method asdefined in claim 1 wherein the acidic catalytic composite contains, onan elemental basis, about 0.05 to about 1 wt. % platinum group metal,about 0.05 to about 1 wt. % ruthenium, about 0.05 to about 1 wt. %rhenium and about 0.5 to about 1.5 wt. % halogen.
 23. A method asdefined in claim 1 wherein the metals content of the catalytic compositeis adjusted so that the atomic ratio of ruthenium to platinum groupmetal is about 0.1:1 to about 5:1 and the atomic ratio of rhenium toplatinum group metal is about 0.1:1 to about 10:1.
 24. A method asdefined in claim 1 wherein the contacting is performed in asubstantially water-free environment.